The invention relates to a two-position seat valve with a valve body comprising the connections for the medium to be controlled and a switching member movable for switching purposes in an axial direction in the valve body and comprising at least one sealing region which lies in a plane substantially perpendicular to the direction of movement of the switching member, and which when in its closed position lies against a substantially facing fixed sealing region on the valve body, the connections for the medium to be controlled opening into the body interior on one and the other side of the fixed sealing region.
In order to amplify to a maximum extent the low control energy available in particular in pneumatic systems, directional valves are used having a large nominal diameter and a small control medium requirement for their operator elements. In the case of valves with diaphragm operators this means a somewhat small diaphragm diameter, a small life, low control pressure and a small clearance.
With seat valves it is certainly possible to switch large nominal diameters using a small operating element lift, but this means that all the noted requirements cannot be fulfilled. In the case of diaphragm valve operation, in order to be able to manage with low control pressure with a small diaphragm area, the seat valve must be able to be operated using minimun switching force. In the present state of the art the most suitable type for fulfilling all the aforesaid requirements is a pressure equalizing valve, the basic construction of which is well known - see for example EP 0 110 139 B1. The advantage of the pressure equalizing valve is that the air pressure has no influence on the required switching force. Drawbacks are the relatively large forces required for sealing against the seats and overcoming the switching friction, and the lifts deriving from the different tolerances, for compensating which the clearances have to be increased.
The object of the invention is to so improve a two-position seat valve of the aforesaid type as to obviate the noted drawbacks of known arrangements and in particular to provide by simple and cost-effective means a valve which requires only low control energy while at the same time operating satisfactorily.